A technique is known in which in a computer system, a real page is allocated from a pool including a plurality of real storage areas (hereinafter referred to as “real pages”) to a write destination virtual page in a virtual volume (a virtual logical volume) including a plurality of virtual storage areas (hereinafter “virtual pages”) and write target data is written to the allocated real page. This technique is typically a kind of Thin Provisioning. A tiered pool is known as a kind of pool. The tiered pool is a storage area including a plurality of real page groups having different input/output performance (IO performance). Generally, one real page group is based on one or more storage devices having the same IO performance (or similar IO performance).
Hereinafter, each layer in the tiered pool is referred to as a “storage tier”. The storage tier corresponds to a real page group. In other words, a plurality of real page groups having different IO performance correspond to a plurality of storage tiers respectively.
Changing a real page allocated to a virtual page, more specifically, migrating data of a target virtual page from a migration source real page allocated to the target virtual page to a migration destination real page in a storage tier different from a storage tier including the migration source real page and allocating the migration destination real page instead of the migration source real page to the target virtual page may be hereinafter referred to as “page migration”. In the page migration, data is migrated by a page unit. Hereinafter, data of a page unit, which is migrated by the page migration, may be referred to as “page data”. If it is not necessary to migrate the data of the migration source real page to the migration destination real page, the data need not be migrated in the page migration.
A data object is stored in such a virtual volume. Examples of the data object include “data set” which is a data object managed by a host computer of a main frame system and “file” which is a data object managed by a host computer of an open system.
Examples of technique related to data management in the tiered pool include techniques disclosed in Patent Literature 1 to Patent Literature 4.